Exhaust gas heat exchanger and method for the production thereof

ABSTRACT

The invention relates to an exhaust gas heat exchanger for motor vehicles, comprising a cluster of exhaust pipes ( 10 ) which are soldered on the front surface thereof to pipe bottoms, and a housing jacket ( 3, 3   b ) which is welded to the pipe bottoms ( 7 ). According to the invention, the pipe bottoms are welded to the housing jacket ( 3   b ) by means of peripheral welds ( 11 ).

BACKGROUND OF THE INVENTION

The invention relates to an exhaust gas heat exchanger for motorvehicles, of the same type which is known from commonly assigned DE-A199 07 163. The invention also relates to a method for production of anexhaust gas heat exchanger such as this.

DE-A 199 07 163 discloses a welded exhaust gas heat exchanger whichcomprises a housing casing, a pipe or tube bundle and pipe bases (headerplates), with the ends of the pipes being welded in the pipe bases andthe pipe bases being welded via circumferential beads to the housingcasing. The pipe ends are welded in the pipe base at the ends, while thepipe bases are welded circumferentially to the housing casing, that isto say the laser beam which is used for the welding process is directedat right angles to the pipe axes. In this case, the laser beam is eitherpassed around the housing or the laser beam is stationary and thehousing is rotated about its longitudinal axis. The different weldingdirections (with respect to the direction of the laser beam) make itnecessary to clamp the workpiece, that is to say the heat exchangerblock, at least twice successively. This increases the productioncomplexity. Furthermore, in the known production method, provision ismade for the heat exchanger block, that is to say the housing casing,not to be cut to length until two circumferential weld beads have beenapplied, to be precise by means of an additional laser beam step. Thisalso involves additional production complexity.

One object of the present invention is to improve the welding carriedout on an exhaust gas heat exchanger of the type mentioned initially.Another object of the invention is to provide a simplified method forits production, in particular for welding of this exhaust gas heatexchanger.

SUMMARY OF THE INVENTION

This object is achieved by the present invention. According to oneembodiment of the present invention, both welded joints can be produced,that is to say the pipe/pipe base joint and the pipe base/housing casingjoint, can be produced in a jig for the heat exchanger block, i.e.,effectively in one operation. Both weld beams can be produced from theend face of the heat exchanger block, so that the block needs not bemoved in the jig. Furthermore, this avoids the additional process stepof cutting the housing casing to length by using the welding tool forcutting, so that the housing casing is cut to length even before thewelding process.

According to one advantageous refinement of the invention, the pipe baseis pot-shaped, that is to say it is provided with a raised rim, whichends flush with the housing casing and can thus be welded to the housingcasing relatively easily by means of a circumferential bead.

The production method according to the invention reduces the unit costsof the exhaust gas heat exchanger, because the production times arereduced. The heat exchanger block, comprising pipes, pipe bases and thehousing casing, is first of all assembled with the housing casingalready having been cut to length. The heat exchanger block is thenplaced in a jig and the end welding is carried out by means of acircumferential bead and a large number of pipe beads. Since the weldingis carried out from one and the same side, specifically from the end,all the weld beads can be made parallel to one another, that is to sayeffectively at the same time. This further reduces the production times.

One exemplary embodiment of the invention will be described in moredetail in the following text and is illustrated in the drawing, inwhich:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exhaust gas heat exchanger,

FIG. 2 shows a section through the end area of the exhaust gas heatexchanger,

FIG. 3 shows a detail X from FIG. 2,

FIG. 4 shows the exhaust gas heat exchanger with its individual partsillustrated in an exploded form,

FIG. 5 shows the end welding of the circumferential bead, and

FIG. 6 shows the end welding of the pipe/pipe base beads.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exhaust gas heat exchanger 1 which can be used as anexhaust gas cooler for cooling down exhaust gases when exhaust gasfeedback is in use. A housing casing 2, made of stainless steel sheet,has two end areas 3 and 4 with a slightly wider cross section and whicheach have a coolant inlet opening 5 and a coolant outlet opening 6. Apipe base 7 is inserted into the end area 3 on the right in the drawingand has uniformly arranged rectangular openings 8 into which pipe ends,which are not illustrated here, of a pipe bundle are inserted.

FIG. 2 shows the end area 3 from FIG. 1 in the form of a longitudinalcross section through the coolant aperture opening 6. The pipe base 7 isinserted into the end area of the housing casing 2 such that it isflush, and thus forms a common end plane 9. Exhaust pipes 10 areinserted into the openings 8 in the pipe base 7, although only some ofthe pipes 10 from the entire pipe bundle are illustrated. Exhaust gasflows through the inside of these exhaust pipes 10, with coolant flowingaround their outside, which coolant is taken, for example, from acoolant circuit (which is not illustrated) for an internal combustionengine in the motor vehicle.

FIG. 3 shows a detail X from FIG. 2, that is to say the end rim area ofthe pipe base 7 and end area 3 of the housing casing 2. In its rim area,the pipe base 7 has a rim 7 a which is raised approximately at rightangles, rests circumferentially against the inner surface 3 a of the endarea 3, and ends flush at the end with the housing casing 2 or its end 3b, to be precise on the end plane 9. The rim 7 a of the pipe base 7 andthe end area 3 b of the housing casing 2 are connected to one another ina sealed form by means of an end weld bead, which extends axially fromend plane 9 to form a so-called circumferential bead 11. Thecircumferential bead 11 is welded through, that is to say it extends toa depth t; it may also only be welded in, that is to say to a depth lessthan t. The pipe 10 has a pipe end 10 a, which ends approximately flushwith the pipe base 7 and is connected to the pipe base 7 by means of aweld bead 12. The weld bead 12 is welded through, that is to say itextends over the entire thickness of the pipe base 7. However,alternatively, it is possible to just weld in the pipe end 10 a, as isillustrated in the drawing as an alternative bead 12, which is notwelded in so deeply. All of the pipes, 10 are connected to the pipe base7 by means of a weld bead 12 in the same way. The weld beads 11, 12 and12′ are each produced from the end face of the exhaust gas heatexchanger 1, as will be described in more detail in the following text.

FIG. 4 shows a slightly modified exhaust gas heat exchanger 20 with ahousing casing 21, two pipe bases 22, 23 and a pipe bundle 25 whichcomprises nine exhaust pipes 24, all in the form of an explodedillustration. The exhaust gas heat exchanger 1 or 20 is now produced insuch a way that the heat exchanger block, comprising a housing casing20, the pipe bundle 25 and the pipe bases 22, 23 are first mechanicallyjoined and assembled. During this process, the pipe ends are insertedinto the pipe bases 22, 23, and the latter are inserted into the endfaces of the housing casing 20. As mentioned above, the housing casing20 has already been cut to length.

FIG. 5 shows the completely assembled block 20′ which is held in aclamping apparatus 40 (schematically shown), arranged, for example,vertically. A laser beam welding apparatus is located above the pipebase 23, that is to say in an end extension of the block 20′, and isrepresented schematically by an ellipse 26. This welding apparatus 26produces a laser beam 27 which produces the circumferential bead 11illustrated in FIG. 3, that is to say it produces the joint between thepipe base 7 and the housing casing 2 by moving around the circumferenceonce. The laser beam may in this case be at right angles to, or slightlyinclined with respect to, a block axis.

FIG. 6 shows, once again schematically, a welding apparatus 28 fromwhich a laser beam 29 is directed at the end face of the heat exchangerblock 20″. This laser beam 29 produces the weld beads 12 (see FIG. 3) bymoving around the circumference of each pipe end. For the sake ofsimplicity, only one laser beam 29 is illustrated here, although anumber of laser beams may be used at the same time, that is to say amaximum number corresponding to the number of pipes 10. The heatexchanger block 20″ illustrated in FIG. 6 is likewise held in a clampingapparatus (which is not illustrated), that is to say in the same way asin FIG. 5. The heat exchanger block 20′ or 20″ therefore need be clampedin only once to produce the weld beads 11 and 12. The weld beads 11 and12 need not be produced successively but in fact can be producedsynchronously, that is to say they can be produced approximately at thesame time, thus reducing the production times.

1. An exhaust gas heat exchanger suitable for use in a motor vehicle,comprising: at least one header plate; a bundle of exhaust gas tubeswhich are welded at least at one end to the at least one header plate;and a housing casing which is welded to the at least one header plate,wherein the at least one header plate is welded to the housing casingvia a circumferential bead which is arranged at one end surface of thehousing casing, and wherein the circumferential bead extends axiallyfrom said end surface to a given depth between the housing casing andthe header plate.
 2. The exhaust gas heat exchanger as claimed in claim1, wherein the at least one header plate comprises a raised rim, whereinthe rim and the end surface of the housing casing is arranged contiguousto one another and are joined by the circumferential bead.
 3. A methodfor production of an exhaust gas heat exchanger that comprises at leastone header plate, a bundle of exhaust gas tubes which are welded atleast at one end to the at least one header plate, and a housing casingwhich is welded to the header plate via a circumferential weld beadwhich is arranged at an end surface of the housing casing, saidcircumferential bead extending axially from said end surface to a givendepth between the housing casing and the header plate the methodcomprising: assembling the exhaust gas tubes, the at least one headerplate and the housing casing into the configuration of a heat exchangerblock; clamping a configuration of the heat exchanger block intoposition in a clamping device; and welding to each other (1) the housingcasing and the at least one header plate, to form the circumferentialweld bead, and also (2) the exhaust gas tubes and the at least oneheader plate, while the configuration is clamped in the same position inthe clamping device.
 4. The method as claimed in claim 3, wherein thewelding is carried out by at least one laser beam.
 5. A method asclaimed in claim 3, wherein the at least one header plate has a raisedrim, and wherein the rim and the end surface of the housing casing arearranged to be contiguous and are connected together by thecircumferential bead.